The response of human T lymphocytes against alloantigens following Fas-mediated activation-induced cell death

We examined the response of T lymphocytes activated with specific alloantigens following Fas-mediated apoptosis; using a mixed lymphocyte culture (MLC) system. Cells obtained from an MLC after 6 or 7 days of culture were incubated for are additional 24 hours in the presence or absence of the agonistic monoclonal antibody (MoAb), 7C11, or the antagonistic MoAb, ZB4. We assessed DNA fragmentation/specific cytotoxiy of the MoAb-treated cells. Cells harvested after 4 days of culture were sensitive to apoptosis induced by 7C11 with maximum DNA fragmentation observed on day 6. ZB4 slightly inhibited apoptosis of the cells compared with controls. The simultaneous addition of recombinant interleukin-2 (rIL-2) with the MoAbs significantly inhibited DNA fragmentation in control and ZB4-treated cells, but had little effect on the 7C11-treated cells. Control and ZB4-treated MLC cells showed cytotoxic activities against specific target cells, namely >10%. In contrast, the 7C11-treated cells showed <5% cytotoxicity. Although the addition of rIL-2 increased specific percentage cytotoxicity of control and ZB4-treated cells, it had little effect on the specific cytotoxic activity of the 7C11-treated MLC cells. These results suggest that specific cytotoxic T lymphocytes may be eliminated via apoptosis mediated by the Fas/Fas ligand system.